July 5 - 7, 2013
Friday, July 5
How to find NGC 5634, M5, NGC 5897, NGC 5694 and NGC 6946, the Fireworks Galaxy this weekend.
This weekend is all about fireworks, so make sure to take the time to enjoy some celestial ones too! To the eye, one of the most splendid signs of the changing seasons is the Ursa Major Moving Group which sits above Polaris for northern hemisphere observers. For the southern hemisphere, the return of Crux serves the same purpose.
NGC 5634 - Palomar Observatory Courtesy of Caltech
Old favorites have now begun to appear again, such as Hercules, Cygnus and Scorpius, and with them a wealth of starry clusters and nebulae that will soon come into view as the night deepens and the hour grows late.
Before we leave Virgo for the year, there is one last object that is seldom explored and such a worthy target that we must visit it before we go. Its name is NGC 5634 and you'll find it halfway between Iota and Mu Virginis (RA 14 29.37 Dec -05 58.35).
First discovered by Sir William Herschel on March 5, 1785, and cataloged as H I.70, this magnitude 9.5 small globular cluster isn't for everyone, but thanks to an 11th magnitude line-of-sight star on its eastern edge, it sure is interesting. At class IV, it's more concentrated than many globular clusters, although its 19th magnitude members make it near impossible to resolve with backyard equipment.
Located a bit more than 82,000 light-years from our solar system and about 69,000 light-years from the galactic center, you'll truly enjoy this globular for the randomly scattered stellar field which accompanies it. In the finderscope, an 8th magnitude star will lead the way - not truly a member of the cluster, but one that lies between us. Capturable in scopes as small as 4.5″, look for a concentrated central area surrounded by a haze of stellar members - a huge number of which are recently discovered variables.
While you look at this globular, keep this in mind... Based on observations with the Italian Telescopio Nazionale Galileo, it is now surmised that the NGC 5634 globular cluster has the same position and radial velocity as does the Sagittarius dwarf spheroidal galaxy. Because of the dwarf galaxy's metal-poor population of stars, it is believed that NGC 5634 may have once been part of the dwarf galaxy - and been pulled away by our own tidal field to become part of the Sagittarius stream!
Saturday, July 6
Tonight we make the jump to Serpens Caput, which is in itself a challenge to recognize with the unaided eye. Using bright Spica as a guide, look about a handspan to its northeast for two of the brightest stars in the constellation - Alpha, and Lambda to its northeast. Using binoculars, locate a pairing with Delta to the north-northwest and Mu to the south. Now return to Alpha and hop a little less than a fistwidth to the southwest where you will encounter double star 5 Serpens and the mighty Messier 5, or M5, (Right Ascension: 15:18.6 - Declination: +02:05).
While Gottfried Kirch and his wife Maria were watching a comet on May 5, 1702, they stumbled across a huge, bright object that they considered a "nebulous star." Forty-two years later, it was found again by Messier who labeled it as M5 and described it as a round nebula which didn't contain any stars. But, thank heaven for William Herschel! Some 27 years later he counted up to 200 resolvable stars in this globular cluster and reported "the middle is so compressed that it is impossible to distinguish the components."
M5 - Credit: Hillary Mathis, REU Program/NOAO/AURA/NSF
Even in today's binoculars, M5 shows a grainy texture that begins resolution to even the smallest of telescopes and invites larger ones to an explosion of stellar population. Slightly elliptical in appearance, M5 is believed to be one of the oldest globular clusters with a calculated age of 13 billion years, and it contains 105 known variable stars - as well as a dwarf nova. At a distance of 24,500 light-years and stretching across 165 light-years of space, this magnificent object so dominates its territory that it would gather in any stars straying within 400 light-years of its tidal influence!
Mid-to-larger telescopes will begin such awesome resolution on M5′s many chains and its bright core region that it will be a cluster you will visit again and again over the years. No matter what size binoculars or telescope you use, this 5.6 magnitude class V globular cluster is one of the five brightest in the sky!
Sunday, July 7
Tonight, let's go globular again and hunt up two very nice studies worthy of your time. Starting at Alpha Librae, head five degrees southeast for Tau and yet another degree southeast for the splendid field of NGC 5897 (RA 15 17 24.40 Dec -21 00 36.4).
This class XI globular might appear very faint to binoculars, but it definitely makes up for it in size and beauty of field. It was first viewed by William Herschel on April 25, 1784 and logged as H VI.8 - but with a less than perfect notation of position. When he reviewed it again on March 10, 1785 he logged it correctly and relabeled it as H VI.19.
At a distance of a little more than 40,000 light-years away, this 8.5 magnitude globular will show some details to the larger telescope, but remain unresolved to smaller ones. As a halo globular cluster, NGC 5897 certainly shows signs of being disrupted and has a number of blue stragglers as well as four newly discovered variables of the RR Lyrae type.
NGC 5694 - Palomar Observatory Courtesy of Caltech
Now let's return to Alpha Librae and head about a fistwidth south across the border into Hydra and two degrees east of star 57 for NGC 5694 - also in an attractive field (RA 14 39 36.52 Dec -26 32 18.0).
Also discovered by Herschel, and cataloged as H II.196, this class VII cluster is far too faint for binoculars at magnitude 10, and barely within reach of smaller scopes. As one of the most remote globular clusters in our galaxy, few telescopes can hope to resolve this more than 113,000 light-year distant ball of stars&mash;the brightest of which has a magnitude of 16.5. It also possesses no variables.
Traveling at 190 kilometers per second, metal-poor NGC 5694 will not have the same fate as NGC 5897... for this is a globular cluster that is not being pulled apart by our galaxy, but escaping it!
Weekend Bonus: The Fireworks Galaxy, NGC 6946
Want to celebrate Independence Day with a real bang? Then if you're a northern viewer, try your hand at a galaxy that has more documented supernovae events than any other - NGC 6946 (RA 20 34 51 Dec +60 09 18).
Located in Cepheus and known as the "Firecracker Galaxy", this faint beauty was discovered by William Herschel on September 9, 1798. Don't expect it to dazzle your eyes, though... The 10 million-light-year-distant face-on spiral NGC 6946 spreads itself pretty thin in modest instruments. Lacking a bright core, this oval mist orients southwest to northeast. Larger telescopes will reveal traces of rotating spiral arms, especially in the southwest. This galaxy would appear extraordinary if we weren't looking through Milky Way obscuration to view it!
Until next week? Dreams really do come true when you keep on reaching for the stars!
Did you try any of these targets? Tell us about your favorites in the comments!
Tammy Plotner is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She's received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.